Degree of Polymerization (DP) Result

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Methods for drying the paper (and oil) insulation of a transformer, no matter what the approach, cannot improve the DP. DP is a measure of how much the polymeric structure of the cellullose paper insulation has deteriorated over time due to chemical and thermal influences. If you want to produce good DP when it is already bad, you need to rewind the transformer. If you want to prevent a transformer whose DP is deteriorating from getting worse, you need to eliminate or reduce the factors that are causing the deterioration (heat, dissolved moisture, acidic radicals in the oil, etc.).

hi Peter,

Thanks for the explanation. Maybe i have put wrong word of " produce " , sorry about that.

As mentioned in your reply, drying process has purpose to eliminate/reduce the factors that are causing deteriotation such as moisture,etc. I therefore become confused, which process is more effective in regards to this purpose? Is it Vapour Phase or Hot Air Circulation?

since at the end of the drying process,these methods will influence DP level. Is that correct?

hi Guest,

yes, drying process will have some "influence" for the DP result since it will later affect dryness of insulation materials used in the transformers. If the insulation materials is dried enough than moisture will hardly penetrate its layer and can not cause deteriotation (even we can't be sure 100% of it). This assumption is made without considering oil presence which also can strengthen insulation materials's barrier to moisture.

According to my experience,i would prefer to use VP drying instead of only hot air circulation since kerosene is proven to be more effective to "bond" moisture inside insulation materials and then "release" it in the drying chamber than hot air. It is also release good heat energy (approx.306.6kJ/kg) than hot air only which do not cause insulation materials over-heated.

DP measurement result is quite different, 995 (VP) vs 960 (Hot air).

Hai,

As "DJ" saying absolutly correct. You can send the TX near any TX manufacturing company and they will process in Vacuum oven @ 90 + deg C temp and servicing the complete TX.

It impoves dryness of winding and the detoriation of paper stops at that point.

The detoriation causes due to over heat. Pls try to arrange extra cooling system to discussed with vendor and avoid further problems.

For typical power transformer, with an oil to paper ratio of 20:1, the 2-furaldehyde levels have the following significance:

I hope this helps some extent

I am not a polymer or chemist but my polymer engineer explained me degree of polymerization is effectively conversion of monomer to polymer. Polymer when starts growing its Molecular weight by converting monomer to polymeric structure. This growth will continue till active sites are feed ed with small molecule. This is the DP. Then comes degree of depolarization or polymer degradation which is breaking those bond and degrading the polymeric properties like adhesion weather resistance and dielectric constant.

Degree of polymerization is calculated using area in the crystallization curve.

If what "DJ46" recommends is possible (sending Transformer out for VF drying), then I agree that it would be better than hot air drying. If not possible, then the best alternative on location is vacuum / hot oil processing. The old oil is removed from the transformer. Vacuum is drawn on the transformer tank (with core/coils in place), per Mfr's recommended. Once vacuum has been held for adequate time to draw moisture out of paper & windings (often 8-24 hours), then heated new insulating oil is pumped in while the vacuum is still held. This draws any dissolved water out of the oil before it can infiltrate the paper again.

Note too that when you process or replace the oil, your DP test results will be inaccurate for a time, until any furanic compounds present in the paper come to equilibrium in the oil.